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Yes I think it's a pleonasm but the problem is not being or not beign a pleonasm but that it sounds strange and even artificial. Maybe it's a reginalism but I doubt you would ever hear a native (at least in Spain) using it.
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LauraFeb 22 '12 at 15:50

@Laura I think the problem is that "mas" is less used than "pero". It's common to read things like "Mario tiene que hacer muchas tareas, pero sin embargo está jugando."
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JaviFeb 22 '12 at 16:05

@Javi wouldn't be that a pleonasm too or is it used to make more emphasis?
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Alfredo OsorioFeb 22 '12 at 16:08

@AlfredoO I think "pero sin embargo" is also a pleonasm. By the way, aren't pleonasms a way of emphasizing?
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JaviFeb 22 '12 at 16:12